Probe card and method for testing magnetic sensors

ABSTRACT

A probe card and method are provided for testing magnetic sensors at the wafer level. The probe card has one or more probe tips having a first pair of solenoid coils in parallel configuration on first opposed sides of each probe tip to supply a magnetic field in a first (X) direction, a second pair of solenoid coils in parallel configuration on second opposed sides of each probe tip to supply a magnetic field in a second (Y) direction orthogonal to the first direction, and an optional third solenoid coil enclosing or inscribing the first and second pair to supply a magnetic field in a third direction (Z) orthogonal to both the first and second directions. The first pair, second pair, and third coil are each symmetrical with a point on the probe tip array, the point being aligned with and positioned close to a magnetic sensor during test.

TECHNICAL FIELD

The exemplary embodiments described herein generally relate to magneticsensors and more particularly to a probe card and a method for testingintegrated magnetic sensors.

BACKGROUND

Sensors are widely used in modern systems to measure or detect physicalparameters, such as direction, position, motion, force, acceleration,temperature, and pressure. While a variety of different sensor typesexist for measuring these and other parameters, they all suffer fromvarious limitations. For example, inexpensive low field sensors, such asthose used in an electronic compass and other similar magnetic sensingapplications, may comprise anisotropic magnetoresistance (AMR) baseddevices. In order to arrive at the required sensitivity and reasonableresistances that mesh well with complementary metal-oxide semiconductors(CMOS), the chip area of such sensors are generally in the order ofsquare millimeters in size. Furthermore, large set-reset pulses frombulky coils of approximately 500 mA are typically required. For mobileapplications, such AMR sensor configurations are costly in terms ofexpense, circuit area, and power consumption.

Other types of sensors, such as magnetic tunnel junction (MTJ) sensors,giant magnetoresistance (GMR) sensors, and the widely used Hall effectsensors have been used to provide smaller profile sensors, but suchsensors have their own concerns, such as inadequate sensitivity and thetemperature dependence of their magnetic field response. To addressthese concerns, MTJ, GMR, and AMR sensors have been employed in aWheatstone bridge structure to increase sensitivity and to reduce thetemperature dependent resistance changes. Hall effect sensors haverecently become competitive in this type of application through thedevelopment of high sensitivity silicon (Si) based sensors coupled witha thick nickel iron (NiFe) magneto-concentrator for amplification of thelocal magnetic field. These Hall effect devices typically employ thecurrent spinning technique for optimal temperature response, resultingin a larger than desired CMOS footprint for the circuitry associatedwith the multiplexing between the various tap point functionality. Forminimal sensor size, cost and high performance, MTJ sense elements arepreferred.

As a result of the manufacturing process variations, low fieldWheatstone bridge based magnetic sensors may exhibit a small yetvariable residual offset. Temperature shifts, mechanical stress, and theaging of the device may cause small changes in this offset. Furthermore,conventional magnetic sensors have a sensitivity built into the deviceby factors such as sense layer thickness, shape, and flux concentratorgeometry. Therefore, small variations in the manufacturing process maycreate variations in the sensor parameters and therefore create a needfor the magnetic sensors be tested and calibrated for optimalperformance.

Wafer probe cards provide the ability to sort good and bad devices atwafer level to avoid the additional expense of continuing the test andassembly process to a later stage before identifying a poorly performingdevice. By using printed circuit board probe cards, manufacturers obtainelectrical data from the IC devices prior to separating, bonding, andpackaging each IC device on the wafer. This data permits a manufacturerto monitor the manufacturing process, to respond to processing problems,and to make process adjustments before incurring additionalmanufacturing costs. Additionally, other ICs in a multichip module thatmay be paired with a bad device can be preserved for assembly inpackages where all devices are known to be good, instead of requiringother good IC's to be disposed of along with the single poorlyperforming IC.

Testing of three axis magnetic sensors requires a probe card to supplyuniform and adjustable magnetic fields in all three directions at theprobe tip locations where the magnetic sensors are to be tested. Someknown probe card designs use a spiral coil embedded on a printed circuitboard to supply magnetic fields; however, these designs have non-uniformfields at the location of the magnetic sensor devices. The probe cardgeometry is challenging as no parts of the magnetic coil system maypenetrate the plane of the wafer, so the well known Helmholtz geometryfor high spatial uniformity is not available. A large uniformity isdesirable as it allows greater degrees of parallelism in measurement,i.e., the same or very similar field may be applied to multiple devices.Another desirable feature in the design of the coil set for a probe cardis lack of a ferromagnetic core as such cores generally have someremanence, resulting in a residual field imposed on the device after afield excursion, and rendering assessment of the sensors hysteresisbehavior difficult.

Accordingly, it is desirable to provide an inexpensive low field sensorprobe card for testing integrated magnetic sensors. Furthermore, otherdesirable features and characteristics of the exemplary embodiments willbecome apparent from the subsequent detailed description and theappended claims, taken in conjunction with the accompanying drawings andthe foregoing technical field and background.

BRIEF SUMMARY

An inexpensive low field sensor probe card is provided for testingintegrated magnetic sensors.

A first exemplary embodiment of the probe card comprises a probe ringhaving a plurality of probe tips configured to be applied to a pluralityof input nodes and a plurality of output nodes. First and secondsolenoid coils in a non-coaxial arrangement at first and second opposedsides of the probe ring are configured to create a first and a secondmagnetic field, respectively; and third and fourth solenoid coils in anon-coaxial arrangement at third and fourth opposed sides of the probering are configured to create a third and a fourth magnetic field,respectively, the third and fourth magnetic fields being orthogonal tothe first and second magnetic fields.

A second exemplary embodiment comprises a plurality of electricalcontacts configured to be applied to input and output nodes; first andsecond solenoid coils in a non-coaxial arrangement at first and secondopposed sides of the probe ring and configured to create a first and asecond magnetic field, respectively; and third and fourth solenoid coilsin a non-coaxial arrangement at third and fourth opposed side of theprobe ring and configured to create a third and a fourth magnetic field,respectively, the third and fourth magnetic fields being orthogonal tothe first and second magnetic fields.

A third exemplary embodiment comprises a method of testing a magneticsensor with a probe card including a plurality of probe tips and firstand second pairs of non-coaxial coils, comprising applying a firstmagnetic field to the magnetic sensor with the first pair of non-coaxialcoils positioned on first opposed sides of the probe tip; sensing anoutput from the magnetic sensor; applying a second magnetic field withthe second pair of non-coaxial coils positioned on second opposed sidesof the probe tip, the second magnetic field being orthogonal to thefirst magnetic field at the magnetic sensor; and sensing an output fromthe magnetic sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will hereinafter be described in conjunction withthe following drawing figures, wherein like numerals denote likeelements, and:

FIG. 1 illustrates an electronic compass structure which usesdifferential sensors formed from three bridge structures with MTJsensors;

FIG. 2 is a top view of a probe board in accordance with an exemplaryembodiment;

FIG. 3 is a perspective view of the probe board of FIG. 2;

FIG. 4 is a schematic view of a magnetic field generated by a first pairof coils of FIG. 2;

FIG. 5 is a schematic view of a magnetic field generated by a secondpair of coils of FIG. 2;

FIG. 6 is a schematic view of a magnetic field generated by the thirdset of coils of FIG. 2; and

FIG. 7 is a flow chart of an exemplary method for testing magneticsensors.

DETAILED DESCRIPTION

The following detailed description is merely illustrative in nature andis not intended to limit the embodiments of the subject matter or theapplication and uses of such embodiments. Any implementation describedherein as exemplary is not necessarily to be construed as preferred oradvantageous over other implementations. Furthermore, there is nointention to be bound by any expressed or implied theory presented inthe preceding technical field, background, brief summary, or thefollowing detailed description.

A probe card is provided including a probe ring carrying one or moreprobe tips having a first pair of solenoid coils in parallelconfiguration on first opposed sides of the probe tip to supply amagnetic field in a first (X) direction, a second pair of solenoid coilsin parallel configuration on second opposed sides of the probe tip tosupply a magnetic field in a second (Y) direction orthogonal to thefirst direction, and optionally a third solenoid coil enclosing thefirst and second pair to supply a magnetic field in a third direction(Z) orthogonal to both the first and second directions. An alternateembodiment comprises the third solenoid coil inscribed within the firstand second pair. The first pair, second pair, and third coils are eachabout symmetrical with a point on the probe tip, the point being alignedwith and positioned close to a sensor during test.

A magnetic field is provided for all three axes (X, Y, Z) with excellentuniformity. Magnetic remanence is avoided by not using magneticmaterials in the vicinity of the coils or the device under test (DUT) onthe PCB or in the probe structure, and avoiding a ferromagnetic core inthe coils.

During the course of this description, like numbers are used to identifylike elements according to the different figures that illustrate thevarious exemplary embodiments.

It should be noted that all components of this exemplary embodiment asillustrated in FIG. 2 that are similar to components of the exemplaryembodiment of FIG. 1 are designated with like numbers.

While magnetic tunnel junction sensors are described herein, any type ofmagnetic sensor may be tested in accordance with the apparatus andmethod described herein. FIG. 1 shows such an exemplary magnetic fieldsensor 100 formed with first, second, and third differential sensors101, 111, 121 for detecting the component directions of an applied fieldalong a first axis 120 (e.g., the y-axis direction), a second axis 110(e.g., the x-axis direction), and a third axis 130 (e.g., the z-axisdirection), respectively. The z-axis direction is represented as a dotand cross-hairs as going either into or out of the page on which FIG. 1is situated. Exemplary embodiments of the first and second sensors 101,111 are described in detail in U.S. patent application Ser. No.12/433,679. As depicted herein, each sensor 101, 111, 121 is formed withunshielded sense elements that are connected in a bridge configuration.Thus, the first sensor 101 is formed from the connection of a pluralityof sense elements 102-105 in a bridge configuration over a correspondingplurality of pinned layers 106-109, where each of the pinned layers106-109 is magnetized in the x-axis direction. In similar fashion, thesecond sensor 111 is formed from the connection of a plurality of senseelements 112-115 in a bridge configuration over a correspondingplurality of pinned layers 116-119 that are each magnetized in they-axis direction that is perpendicular to the magnetization direction ofthe pinned layers 106-109. Furthermore, the third sensor 121 in the sameplane as the first and second sensors 101, 111 is formed from theconnection of a plurality of sense elements 122-125 in a bridgeconfiguration over a corresponding plurality of pinned layers 126-129that are each magnetized in an arbitrary in-plane direction that may beat any angle to the magnetization directions of the pinned layers106-109 and 116-119. In the depicted bridge configuration 101, the senseelements 102, 104 are formed to have a first easy axis magnetizationdirection and the sense elements 103, 105 are formed to have a secondeasy axis magnetization direction, where the first and second easy axismagnetization directions are orthogonal with respect to one another andare oriented to differ equally from the magnetization direction of thepinned layers 106-109. As for the second bridge configuration 111, thesense elements 112, 114 have a first easy axis magnetization directionthat is orthogonal to the second easy axis magnetization direction forthe sense elements 113, 115 so that the first and second easy axismagnetization directions are oriented to differ equally from themagnetization direction of the pinned layers 116-119. In the thirdbridge configuration 121, the sense elements 122, 123,124, and 125 allhave an easy axis magnetization direction that is orthogonal to thepinned magnetization direction of the pinned layers 126, 127, 128, and129. The third bridge configuration 121 further includes flux guides133, 135 positioned adjacent to the right edge of sense elements 123,125, and flux guides 136, 138 positioned adjacent to the left edge ofsense elements 122, 124, respectively. Flux guides 133, 135, 136, and138 are positioned below sense elements 122-125. The positioning ofthese flux guides 133, 135, 136, and 138 is subsequently described inmore detail in FIG. 2. In the depicted sensors 101, 111, 121 there is noshielding required for the sense elements, nor are any special referenceelements required. In an exemplary embodiment, this is achieved byreferencing each active sense element (e.g., 102, 104) with anotheractive sense element (e.g., 103, 105) using conventional shapeanisotropy techniques to establish the easy magnetic axes of thereferenced sense elements to be deflected from each other by 90 degreesfor the x and y sensors, and referencing a sense element that respondsin an opposite manner to an applied field in the Z direction for the Zsensor. The Z sensor referencing will be described in more detail below.The configuration shown in FIG. 1 is not required to harvest thebenefits of the third sensor 121 structure described in more detail inFIG. 2, and is only given as an example.

By positioning the first and second sensors 101, 111 to be orthogonallyaligned, each with the sense element orientations deflected equally fromthe sensor's pinning direction and orthogonal to one another in eachsensor, the sensors can detect the component directions of an appliedfield along the first and second axes. Flux guides 133, 135, 136, 138are positioned in sensor 121 below the opposite edges of the elements122-125, in an asymmetrical manner between legs 141, 143 and legs 142,144. As flux guides 136, 138 are placed below the sense elements 122,124, the magnetic flux from the Z field may be guided into the XY planealong the left side and cause the magnetization of sense elements 122and 124 to rotate in a first direction towards a higher resistance.Similarly, the magnetic flux from the Z field may be guided by the fluxguides 133 and 135 into the XY plane along the right side of the senseelement and cause the magnetization of sense elements 123 and 125 torotate in a second direction, opposite from the first direction towardsa lower resistance, as these flux guides are located below the senseelements 123, 125. Thus, the sensor 121 can detect the componentdirections of an applied field along the third axis. Although in thepreferred embodiment, the flux guides are in a plane orthogonal to theplane of the field sensor, the flux guides will still function if theangle they make with the sensor is not exactly 90 degrees. In otherembodiments, the angle between the flux guide and the field sensor couldbe in a range from 45 degrees to 135 degrees, with the exact anglechosen depending on other factors such as on the ease of fabrication.

As seen from the foregoing, a magnetic field sensor may be formed fromdifferential sensors 101, 111, 121 which use unshielded sense elements102-105, 112-115, and sense elements 122-125 with guided magnetic fluxconnected in a bridge configuration over respective pinned, orreference, layers 106-109, 116-119, and 126-129 to detect the presenceand direction of an applied magnetic field. With this configuration, themagnetic field sensor provides good sensitivity, and also provides thetemperature compensating properties of a bridge configuration.

The bridge circuits 101, 111, 121 may be manufactured as part of anexisting MRAM or thin-film sensor manufacturing process with only minoradjustments to control the magnetic orientation of the various sensorlayers and cross section of the flux guiding structures. Each of thepinned layers 106-109, 116-119, and 126-129 may be formed with one ormore lower ferromagnetic layers, and each of the sense elements 102-105,112-125, 122-125 may be formed with one or more upper ferromagneticlayers. An insulating tunneling dielectric layer (not shown) may bedisposed between the sense elements 102-105, 112-125, 122-125 and thepinned layers 106-109, 116-119, and 126-129. The pinned and senseelectrodes are desirably magnetic materials whose magnetizationdirection can be aligned. Suitable electrode materials and arrangementsof the materials into structures commonly used for electrodes ofmagnetoresistive random access memory (MRAM) devices and other magnetictunnel junction (MTJ) sensor devices are well known in the art. Forexample, pinned layers 106-109, 116-119, and 126-129 may be formed withone or more layers of ferromagnetic and antiferromagnetic materials to acombined thickness in the range 10 to 1000 Å, and in selectedembodiments in the range 250 to 350 Å. In an exemplary implementation,each of the pinned layers 106-109, 116-119, and 126-129 is formed with asingle ferromagnetic layer and an underlying anti-ferromagnetic pinninglayer. In another exemplary implementation, each pinned layer 106-109,116-119, and 126-129 includes a synthetic anti-ferromagnetic stackcomponent, for example, a stack of Cobalt Iron (CF)/Cobalt Iron Boron(CFB), Ruthenium (Ru), and CFB which is 20 to 80 Å thick, and anunderlying anti-ferromagnetic pinning layer that is approximately 200 Åthick. The lower anti-ferromagnetic pinning materials may be re-settablematerials, such as IrMn, though other materials, such as plantinummanganese (PtMn), can be used which are not readily re-set at reasonabletemperatures. As formed, the pinned layers 106-109, 116-119, and 126-129function as a fixed or pinned magnetic layer when the direction of itsmagnetization is pinned in one direction that does not change duringnormal operating conditions. As disclosed herein, the heating qualitiesof the materials used to pin the pinned layers 106-109, 116-119, and126-129 can change the fabrication sequence used to form these layers.

One of each of the sense elements 102-105, 112-125, 122-125 and one ofeach of the pinned layers 106-109, 116-119, 126-129 form a magnetictunnel junction (MTJ) sensor. For example, for bridge circuit 121, senseelement 122 and pinned layer 126 form an MTJ sensor 141. Likewise, senseelement 123 and pinned layer 127 form an MTJ sensor 142, sense element124 and pinned layer 128 form an MTJ sensor 143, and sense element 125and pinned layer 129 form an MTJ sensor 144.

The pinned layers 106-109, 116-119, and 126-129 may be formed with asingle patterned ferromagnetic layer having a magnetization direction(indicated by the arrow) that aligns along the long-axis of thepatterned reference layer(s). However, in other embodiments, the pinnedreference layer may be implemented with a synthetic anti-ferromagnetic(SAF) layer which at the micron size scale will align the magnetizationof the pinned reference layer along the short axis of the patternedreference layer(s). As will be appreciated, the SAF layer may beimplemented in combination with an underlying anti-ferromagnetic pinninglayer, though with SAF structures with appropriate geometry andmaterials that provide sufficiently strong magnetization, the underlyinganti-ferromagnetic pinning layer may not be required, thereby providinga simpler fabrication process with cost savings.

The sense elements 102-105, 112-125, 122-125 may be formed with one ormore layers of ferromagnetic materials to a thickness in the range 10 to5000 Å, and in selected embodiments in the range 10 to 60 Å. The upperferromagnetic materials may be magnetically soft materials, such asNiFe, CoFe, Fe, CFB and the like. In each MTJ sensor, the sense elements102-105, 112-125, 122-125 function as a sense layer or free magneticlayer because the direction of their magnetization can be deflected bythe presence of an external applied field, such as the Earth's magneticfield. As finally formed, sense elements 102-105, 112-125, 122-125 maybe formed with a single ferromagnetic layer having a magnetizationdirection (indicated with the arrows) that aligns along the long-axis ofthe patterned shapes.

The pinned layers 106-109, 116-119, 126-129 and sense elements 102-105,112-125, 122-125 may be formed to have different magnetic properties.For example, the pinned layers 106-109, 116-119, 126-129 may be formedwith an anti-ferromagnetic film exchange layer coupled to aferromagnetic film to form layers with a high coercive force and offsethysteresis curves so that their magnetization direction will be pinnedin one direction, and hence substantially unaffected by an externallyapplied magnetic field. In contrast, the sense elements 102-105,112-125, 122-125 may be formed with a magnetically soft material toprovide different magnetization directions having a comparatively lowanisotropy and coercive force so that the magnetization direction of thesense electrode may be altered by an externally applied magnetic field.In selected embodiments, the strength of the pinning field is about twoorders of magnitude larger than the anisotropy field of the senseelectrodes, although different ratios may be used by adjusting therespective magnetic properties of the electrodes using well knowntechniques to vary their composition.

The pinned layers 106-109, 116-119, 126-129 in the MTJ sensors areformed to have a shape determined magnetization direction in the planeof the pinned layers 106-109, 116-119, 126-129 (identified by the vectorarrows for each sensor bridge labeled “Pinning direction” in FIG. 1). Asdescribed herein, the magnetization direction for the pinned layers106-109, 116-119, 126-129 may be obtained using shape anisotropy of thepinned electrodes, in which case the shapes of the pinned layers106-109, 116-119, 126-129 may each be longer in the pinning directionfor a single pinned layer. Alternatively, for a pinned SAF structure,the reference and pinned layers may be shorter along the pinningdirection. In particular, the magnetization direction for the pinnedlayers 106-109, 116-119, 126-129 may be obtained by first heating theshaped pinned layers 106-109, 116-119, 126-129 in the presence of aorienting magnetic field which is oriented non-orthogonally to the axisof longest orientation for the shaped pinned layers 106-109, 116-119,126-129 such that the applied orienting field includes a field componentin the direction of the desired pinning direction for the pinned layers106-109, 116-119, 126-129. The magnetization directions of the pinnedlayers are thereby aligned, at least temporarily, in a predetermineddirection. However, by appropriately heating the pinned layers duringthis treatment and removing the orienting field without reducing theheat, the magnetization of the pinned layers relaxes along the desiredaxis of orientation for the shaped pinned layers 106-109, 116-119,126-129. Once the magnetization relaxes, the pinned layers can beannealed and/or cooled so that the magnetic field direction of thepinned electrode layers is set in the desired direction for the shapedpinned layers 106-109, 116-119, 126-129.

An example of a device that may be tested using the exemplaryembodiments include self-test lines 151, 152 formed parallel to the fluxguides 135, 136, respectively, equidistant from the sensors 122, 125.Likewise, self-test lines 153, 154 are formed parallel to the fluxguides 133, 138, respectively, equidistant from the sensors 123, 124.The self-test lines 151-154 are a conductive material, for example,copper (Cu) or aluminum (Al). For example, a magnetoresistive senseelement 122 is formed over a substrate, the magnetoresistive senseelement 122 defining a long axis and a first plane through the longaxis, the plane being perpendicular to the substrate. First and secondself-test current carrying lines 151, 152 are equidistant from, parallelto, and on opposed sides of, the plane; and a flux guide 136 is adjacenta first edge of the first magnetoresistive sense element 122, wherein afirst component of a first magnetic field in the plane of themagnetoresistive sense element 122 created by a first current in a firstdirection in the first self-test current carrying line 151, and a secondcomponent of a second magnetic field in the plane of the sense element122 created by a second current in a second direction in the secondself-test current carrying line 152 cancel one another at theintersection of the first plane and the long axis of themagnetoresistive sense element 122, and the first and second magneticfield components out of the plane of the magnetoresistive sense element122 are additive at the flux guide 136, and a portion of the out ofplane components are guided into the magnetoresistive sense element 122as a third component.

In accordance with an exemplary embodiment for testing the magneticsensors at wafer level and referring to the pictorial top view,pictorial perspective view, and schematic top view of FIGS. 2-4,respectively, a probe card 200 is provided having one or more probe tips201 having a first pair 203, 204 of solenoid coils in a non-coaxialarrangement, parallel in configuration on first opposed sides of theprobe tip 200, a second pair 205, 206 of solenoid coils in a non-coaxialarrangement, parallel in configuration on second opposed sides of theprobe tip 200, and optionally a third solenoid coil 207 eitherencircling (surrounding) or within (or inscribed in) the first andsecond pair of coils 203-206. The solenoid coils 203-206 each have anaspect ratio of length to diameter greater than three and the solenoidcoil 207 has a low aspect ratio of length to diameter of much less than1, and is positioned close to the wafer surface. Each coil 203-207 is aconductor, e.g., a copper wire, wound around a non-ferromagnetic core,and is coupled to the PCB to receive a current for creating a magneticfield. Each of the pairs of coils 203, 204 and 205, 206 are spaced apartby about 3.0 to 10.0 cm, but preferably about 5.0 cm. Preferably, adistance between the first and second coils 203, 204 is greater than thelength of the coils 203, 204. Likewise, a distance between the third andfourth coils 205, 206 is greater than the length of the coils 205, 206.

The probe card 200 may be any type of structure that supports thesolenoid coils 203-207, but preferably is a printed circuit board (PCB).The PCB typically includes a plurality of dielectric insulating layerslaminated together with epoxy resin prepreg (reinforcement materialpre-impregnated with a resin matrix) that allows for the positioning andcoupling of a plurality of electronic components, for example, circuitry212. After the printed circuit board (PCB) is completed, electroniccomponents must be attached to form a functional printed circuitassembly, or PCA (sometimes called a “printed circuit board assembly”PCBA). In through-hole construction, component leads are inserted inholes. In surface-mount construction, the components are placed on padsor lands on the outer surfaces of the PCB. In both kinds ofconstruction, component leads are electrically and mechanically fixed tothe board with a molten metal solder. The coils 203-207 are placed onthe PCB using surface-mount construction in the preferred embodiment.

A spacer, or nest, 201 is positioned on the probe card 200 and withinthe coils 203-207. In operation, the probe card 200 containing one ormore of the probe tips 202 is placed over an integrated circuit of themagnetic sensor 100 or a plurality of magnetic sensors 100. The spacer201 prevents the coils from touching the magnetic sensors 100 andprovides an avenue for a plurality of conductors 209 coupled between themagnetic sensors 100 via probe tips 202, and sensing circuitry 212,which ultimately connect back to test system resources and a controlcomputer for data acquisition. Additional circuitry may also be includedon the probe card 200, for example, a test socket (not shown) that isconfigured to receive a packaged test chip, or circuitry that isconfigured to amplify, filter, phase lock, or phase measure. The probering 211 has a plurality of probe tips 202 positioned for coupling tothe nodes of the sensors 101, 111, 121, for example, input nodes 161,162 and output nodes 163, 164 of sensor 111. The probe tips 202 apply avoltage to, for example the input nodes 161, 162, while sensing thevoltage across the sensor elements 112, 113, 115, 118, for example atoutput nodes 163, 164. The bottom of coils 203-207 and the plane of themagnetic sensor 100 are very close in the Z dimension, preferably about0.1 cm apart, to properly align the magnetic fields with the magneticsensor 100. The conductors 209 provide an input to, and receive anoutput from, the magnetic sensors 100 during wafer level testing.

FIG. 4 is a schematic view of the pair of coils 203, 204 and themagnetic fields 213 and 214, respectively, produced in the horizontal(X) direction 220 through the magnetic sensor 100 (FIG. 1) when acurrent is applied to the coils 203, 204. Likewise, FIG. 5 is aschematic view of the pair of coils 205, 206 and the magnetic fields 215and 216, respectively, produced in the vertical (Y) direction 221through the magnetic sensor 100 when a current is applied to the coils205, 206. Note the horizontal (X) direction 220 is orthogonal to thevertical (Y) direction 221. The magnetic fields 213, 214, 215, 216 areconfigured to be aligned with sensitivity axes 120, 110 of the sensors101, 111. For example, the magnetic fields 213, 214 could be alignedwith the X sense axis, 110 while the magnetic fields 215, 216 would bealigned with the Y sense axis 120.

In the exemplary embodiment, the coils are not coaxial, but rather areseparated by a distance that is perpendicular to a line drawn throughtheir centers so that the field applied at the tested device is reversedin direction from the field created at the solenoid core. The pairs ofcoils add constructively, so it is the field projected by the solenoidsas the flux lines close upon themselves that create the field at themagnetic sensor. This is in contrast to a Helmholtz geometry whereincoil sets are coaxial with one another and the device under test islocated mid way between them along the shared center line. This primaryreason for this geometrical arrangement is the high uniformity in fieldstrength and the angle of the applied field with respect to aperturbation around the design center, given the constraint that no partof the coils may extend below the plane of the wafer. This is especiallyimportant for multisite testing wherein an array of devices may betested at once, and, due to their spatial separation, they may not allexperience identical fields if the spatial variation of the field is atall significant. The drawback to this geometry is that the applied fieldmay not be as high as possible for a given applied current, but ifcareful calculations are taken in the design sufficient field may beapplied to test a typical three axis sensor over its entire linear fieldrange. Since the coils are long in aspect ratio (L/W) greater than atleast 2, the out of plane component from the coil set is small comparedto the in plane component, and therefore the total field at the deviceunder test is dominated by its in-plane component. More importantly,this out of plane component is very weakly dependent on the exactspatial positioning of the device.

FIG. 6 is a schematic view of the optional coil 207 and the magneticfield 217 produced in the Z direction 222 through the magnetic sensor100 when a current is applied to the coil 207. Note the Z direction 222is orthogonal to each of the horizontal (X) direction 220 and thevertical (Y) direction 221. Currents may be applied to the coils 203,204; coils 205, 206; and coil 207 simultaneously or separately. Whilethe magnetic fields are illustrated in the conventional positivedirection (horizontally to the right, vertically up, and into the page),the currents applied to the coils 203-207 could be reversed resulting inthe magnetic fields 213-217 being in the reverse, or conventionallynegative, direction.

FIG. 7 is a flow chart that illustrates an exemplary embodiment of aprocess 700 suitable for wafer level testing of magnetic sensors. Thevarious tasks performed in connection with process 700 may be performedby software, hardware, firmware, or any combination thereof. Forillustrative purposes, the following description of process 700 mayrefer to elements mentioned above in connection with FIG. 3. Inpractice, portions of process 700 may be performed by different elementsof the described system, e.g., a processor, a display element, or a datacommunication component. It should be appreciated that process 700 mayinclude any number of additional or alternative tasks, the tasks shownin FIG. 7 need not be performed in the illustrated order, and process700 may be incorporated into a more comprehensive procedure or processhaving additional functionality not described in detail herein.Moreover, one or more of the tasks shown in FIG. 7 could be omitted froman embodiment of the process 700 as long as the intended overallfunctionality remains intact.

Referring to FIG. 7, the method 700 of testing a magnetic sensor with aprobe card of the type including a plurality of probe tips and first andsecond pairs of non-coaxial coils, comprises applying 702 a firstmagnetic field to the magnetic sensor with the first pair of non-coaxialcoils positioned on first opposed sides of the probe tip; sensing 704 anoutput from the magnetic sensor; applying 706 a second magnetic fieldwith the second pair of non-coaxial coils positioned on second opposedsides of the probe tip, the second magnetic field being orthogonal tothe first magnetic field at the magnetic sensor; and sensing 708 anoutput from the magnetic sensor. The sensing steps may occursimultaneously or sequentially.

Although the described exemplary embodiments disclosed herein aredirected to probe cards and methods for using same, the presentinvention is not necessarily limited to the exemplary embodiments whichillustrate inventive aspects of the present invention. Thus, theparticular embodiments disclosed above are illustrative only and shouldnot be taken as limitations upon the present invention, as the inventionmay be modified and practiced in different but equivalent mannersapparent to those skilled in the art having the benefit of the teachingsherein. For example, the distances and thickness of the described coilsmay deviate from the disclosed values. Accordingly, the foregoingdescription is not intended to limit the invention to the particularform set forth, but on the contrary, is intended to cover suchalternatives, modifications and equivalents as may be included withinthe spirit and scope of the invention as defined by the appended claimsso that those skilled in the art should understand that they can makevarious changes, substitutions and alterations without departing fromthe spirit and scope of the invention in its broadest form.

Benefits, other advantages, and solutions to problems have beendescribed above with regard to specific embodiments. However, thebenefits, advantages, solutions to problems, and any element(s) that maycause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, or essentialfeature or element of any or all the claims. As used herein, the terms“comprises,” “comprising,” or any other variation thereof, are intendedto cover a non-exclusive inclusion, such that a process, method,article, or apparatus that comprises a list of elements does not includeonly those elements but may include other elements not expressly listedor inherent to such process, method, article, or apparatus.

While at least one exemplary embodiment has been presented in theforegoing detailed description, it should be appreciated that a vastnumber of variations exist. It should also be appreciated that theexemplary embodiment or exemplary embodiments are only examples, and arenot intended to limit the scope, applicability, or configuration of theinvention in any way. Rather, the foregoing detailed description willprovide those skilled in the art with a convenient road map forimplementing an exemplary embodiment of the invention, it beingunderstood that various changes may be made in the function andarrangement of elements described in an exemplary embodiment withoutdeparting from the scope of the invention as set forth in the appendedclaims.

1. A probe card for testing a magnetic sensor including a plurality ofinput nodes and a plurality of output nodes, the probe card comprising:a probe ring comprising a plurality of probe tips configured to beapplied to the input and output nodes; first and second solenoid coilsin a non-coaxial arrangement at first and second opposed sides of theprobe ring and configured to create a first and a second magnetic field,respectively; and third and fourth solenoid coils in a non coaxialarrangement at third and fourth opposed sides of the probe ring andconfigured to create a third and a fourth magnetic field, respectively,the third and fourth magnetic fields being orthogonal to the first andsecond magnetic fields.
 2. The probe card of claim 1 further comprising:a fifth solenoid coil having a low aspect ratio of length to diameterpositioned adjacent the surface of the sensor to be measured and thefirst, second, third, and fourth solenoid coils, and configured tocreate a fifth magnetic field, wherein the fifth magnetic field isorthogonal to each of the first, second, third, and fourth magneticfields.
 3. The probe card of claim 2 wherein the fifth solenoid coilsurrounds the first, second, third, and fourth solenoid coils.
 4. Theprobe card of claim 2 wherein the fifth solenoid coil surrounds theprobe ring within the first, second, third, and fourth solenoid coils.5. The probe card of claim 1 wherein the magnetic sensor comprises afirst sense axis and a second sense axis orthogonal to the first senseaxis, and wherein the fields of the first and second magnetic fields aresubstantially aligned with the first sense axis, and the third andfourth magnetic fields are aligned with the second sense axis.
 6. Theprobe card of claim 1 wherein the first, second, third, and fourth coilseach have an aspect ratio of length to diameter greater than three. 7.The probe card of claim 1 wherein a distance between each of the firstand second solenoid coils, and the third and fourth solenoid coils, isgreater than the length of the coils.
 8. The probe card of claim 1wherein each of the first and second solenoid coils, and the third andfourth solenoid coils, are configured to provide a highly uniform fieldin angle and strength, such that for displacements of two millimetersfrom a center point, the field angle deviates by less than one degree,and the field magnitude differs by less than one percent.
 9. The probecard of claim 1 further comprising: sensing circuitry coupled to theprobe tips and configured to be electrically coupled to the sensor nodesfor receiving an output from the magnetic sensor in response to at leastone of current and voltage inputs provided to the input nodes, and amagnetic field applied to the sensor by the coils.
 10. The probe card ofclaim 9 wherein the sensing circuitry further comprises: additionalcircuitry configured to, at least one of the group selected from,amplify, filter, phase lock, or phase measure.
 11. A test fixture fortesting a magnetic sensor, the fixture comprising: a plurality ofelectrical contacts configured to be applied to input and output nodes;first and second solenoid coils in a non-coaxial arrangement at firstand second opposed sides of the probe ring and configured to create afirst and a second magnetic field, respectively; and third and fourthsolenoid coils in a non-coaxial arrangement at third and fourth opposedside of the probe ring and configured to create a third and a fourthmagnetic field, respectively, the third and fourth magnetic fields beingorthogonal to the first and second magnetic fields.
 12. The test fixtureof claim 11 further comprising: a fifth solenoid coil having a lowaspect ratio of length to diameter positioned adjacent to the surface ofthe sensor to be measured and adjacent the first and second solenoidcoils and configured to create a fifth magnetic field, wherein the fifthmagnetic field is orthogonal to each of the first, second, third, andfourth magnetic fields.
 13. The test fixture of claim 11 furthercomprising: a test socket coupled to the electrical contacts, the firstand second solenoid coils, the third and fourth solenoid coils, andconfigured to receive a packaged test chip.
 14. The test fixture ofclaim 11 wherein the fields of the first and second magnetic fields aresubstantially aligned with a first sense axis of the magnetic sensor andthe third and fourth magnetic fields are aligned with a second senseaxis orthogonal to the first sense axis.
 15. The test fixture of claim11, wherein the magnetic sensor comprises input and output nodes, thetest fixture further comprising: sensing circuitry coupled to the probetips and configured to be electrically coupled to the output nodes forreceiving an output from the magnetic sensor in response to at least oneof current and a voltage provided at the input nodes, and a magneticfield applied to the sensor by the coils.
 16. The test fixture of claim15 wherein the sensing circuitry further comprises: additional circuitryconfigured to, consisting of at least one of the group selected from,amplify, filter, phase lock, or phase measure.
 17. A method of testing amagnetic sensor with a probe card including a plurality of probe tipsand first and second pairs of non-coaxial coils, comprising: applying afirst magnetic field to the magnetic sensor with the first pair ofnon-coaxial coils positioned on first opposed sides of the probe tip;sensing an output from the magnetic sensor; applying a second magneticfield with the second pair of non-coaxial coils positioned on secondopposed sides of the probe tip, the second magnetic field beingorthogonal to the first magnetic field at the magnetic sensor; andsensing an output from the magnetic sensor.
 18. The method of claim 17wherein the probe tip further includes a solenoid coil surrounding thefirst and second pairs, the method further comprising: applying a thirdmagnetic field with the solenoid coil, wherein the third magnetic fieldis orthogonal to each of the first and second magnetic fields at themagnetic sensor.
 19. The method of claim 17 wherein the applying stepsoccur simultaneously.
 20. The method of claim 18 wherein the applyingsteps occur sequentially.
 21. The method of claim 17 where multiplemagnetic fields are applied by each of the first and second pair ofnon-coaxial coils.
 22. The method of claim 18 where multiple magneticfields are applied by each of the first and second pair non-coaxialcoils and the solenoid coil.